AVDM - Adventure in Moving

To help you move from Waterloo to the big city, you are considering renting a moving truck. Gas prices being so high these days, you want to know how much the gas for such a beast will set you back.

The truck consumes a full litre of gas for each kilometre it travels. It has a 200 litre gas tank. When you rent the truck in Waterloo, the tank is half full. When you return it in the big city, the tank must be at least half full, or you'll get gouged even more for gas by the rental company. You would like to spend as little as possible on gas, but you don't want to run out along the way.

Input

Input is all integers. The first integer is the distance in kilometres from Waterloo to the big city, at most 10000. Next comes a set of up to 100 gas station specifications, describing all the gas stations along your route, in non-decreasing order by distance. Each specification consists of the distance in kilometres of the gas station from Waterloo, and the price of a litre of gas at the gas station, in tenths of a cent, at most 2000.

Output

Output is the minimum amount of money that you can spend on gas to get you from Waterloo to the big city. If it is not possible to get from Waterloo to the big city subject to the constraints above, print "Impossible".

Example

Input:
500
100 999
150 888
200 777
300 999
400 1009
450 1019
500 1399

Output:
450550

Added by:[Retired] Fendy Kosnatha
Date:2011-03-05
Time limit:1s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Languages:All except: ASM64
Resource:UVa

hide comments
2016-03-01 06:38:15 [Rampage] Blue.Mary
As :D mentioned, you must process input until EOF, and process all the given stations one by one (as if they are all BETWEEN waterloo & big city). At last print the result. In other words, you do DP assuming L = +inf, and take L into consideration only when calculating the final result.

Last edit: 2016-03-01 06:42:48
2011-03-14 16:43:33 :D
It's not only about out-of-bound constrains. You have to give a wrong solution to those cases to get AC. If you properly take them into account it will be a WA. You will also fail if you'll not process gas station from first to last (but in reverse for example).
2011-03-14 15:05:54 Ravi Kiran
I think its a little evil to have cases differing from the given constraints.
I have been spending the last 2 hours trying to "guess" the input style.
I think as :D says, the problem setter must modify the input data to match above constraints or update the problem statement.
RE:I have finally got accepted thanks to sonpascal93 for making it clear.In my AC'ed solution, I read the input till EOF and try to process the fuel stations in the order mentioned(not necessarily ascending distances from Waterloo).Hope it helps.

Last edit: 2011-03-16 06:59:14
2011-03-13 22:34:32 :D
There are some issues with the input data. First of all, they are gas stations placed further than big city. I got WA when I tried to take them into account (going further and then back to fill the tank with lower cost). I got AC when I completely ignored it and, what's important, assumed that big city with the proper distance is the last (so there were negative distances during processing).

Please correct the test data because now only specific way of processing the input can get AC.

Last edit: 2011-03-13 22:41:37
2011-03-08 02:37:32 [Retired] Fendy Kosnatha
@Radhakrishnan :
this is a DP problem, maybe this is easier than ROADTRIP
2011-03-06 09:15:35 Radhakrishnan Venkataramani
DP/RMQ ?
Also what do u think of this problem ROADTRIP ?
2012-02-25 10:28:35 A. Muh. Primabudi
@mas fendy, how is the input terminated ?
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